Magnetron output terminal



Nov. 14, 1950 E. c. oKREss MAGNETRQN UTPUT TERMINAL Filed June 6. 1944 ll. ww 7 l m l MVM ATTORNEY Patented Nov. 14, 1950 TENT .OFFICE MAGNETRNOUTPUT TERMINAL Ernest il. Glrress, Montclair, N. J., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application June 6, 1944, Serial No. 538,971

Claims.

This invention relates to output terminals and more particularly tomagnetron output terminals which feed into a hollow wave guide.

In my prior application, Serial No. 461,135, led October 7, 1942, anoutput terminal is shown wherein energy transition from the coaxialconductor to the wave guide is accomplished as an open line exposed toatmospheric pressure. That structure is accordingly subject to highvoltage gradient in air between the exposed end of the coaxial conductorand surrounding metallic parts. When the device is used at highaltitudes, for instance in an airplane, the high voltage gradient andraried atmosphere combine to cause break-down or sparking between saidexposed end of the coaxial conductor and the surrounding metallic parts.

The present invention contemplates use of a Y proper matching ofimpedances, energy transition, and enclosure in vacuum of parts subjectto high voltage gradients, so as to avoid detrimental effects when thedevice is used under varying conditions oi external atmosphericpressure.

More specifically, an object of the invention is to provide aconstruction presenting proper input admittance to the magnetron invacuum while maintaining a suliciently low standing wave ratio in theremaining portions of the terminal exposed to prevailing atmosphericpressure.

A further object of the invention is to provide a terminal which, in itsentirely, inclusive of the Wave guide in whole or in part, need not bemaintained at vacuum or other xed pressure in order to prevent breakdownin use at high altitudes.

Yet another object of the invention is to mim'- mize the extent oi theregion having to be evacuated and maintained under vacuum, and tootherwise provide a simplied sturdy construction.

Still further objects will appear to those skilled in the art as thedescription progresses both lby direct recitation thereof and byinference from the context.

In the accompanying drawing wherein like numerals of reference indi-catesimilar parts throughout the several views:

Figure 1 is a sectional view of a portion of a magnetron and of a waveguide with my invention associated therewith;

Figure 2 is a sectional view on line II-II of Fig. 1; and

Figure 3 is a sectional view on line III- III of Fig. 1.

In the specific embodiment of the invention i1- lustrated in saiddrawing, the reference numeral I0 designates a part of a knownultra-high frequency generator, here shown as a magnetron,

from which wave energy is derivable through a" coaxial line means whichincludes a current probe or loop I l ofsuitable shape situated within acavity I2 of the generator. The interior of said generator is evacuated.

The desideratum is to transfer energy picked up by the loop II to ahollow wave guide I3 situated exterior to the generator and the hollowinterior or passage of which is not evacuated and accordingly subject tothe prevailing atmospheric pressure and condition where the device is inactual use whether that be next to the earth or at a high altitude wherethe air is more rareed. Wave guides in general are known to the art andconstitute a mean by which electromagnetic energy is propagated from oneplace to another before its ultimate transmission in free space orvutilization in some other instrumentality. Usually wave guides arerectangular in cross-section with one dimension greater than the otherfor purposes of obtaining the desired mode of oscillation andpolarization of the Wave that may be transmitted.

The energy transmission means from generator to wave guide is identifiedby the general appellation thereto of terminal, and it is a feature ofthe present invention to construct this terminal with the part thereofnext the wave guide sealed in order that the part next the generator maybe evacuated with and subject to the same vacuum as the interior` of thegenerator, and to utilize the evacuated region in obtaining the desiredelectrical characteristics for the terminal.

The coaxial line means constituted by said terminal comprises, inaddition to loop II abovementioned, a rod-like portion or inner coaxialmember It, which extends into the wave guide, and tubular portion orYouter hollow member I5 coaxial with the rod portion and extending fromthe generator to the wave guide, and attached to both.

Said tubular portion I5 is constituted by a conductive base or thimbleI6 which is hollow and preferably formed as a body of revolution. Oneend of said thimble I6 has a threaded neck or basal' portion Il whichscrews into a side opening for the purpose in the magnetron and sealed,as by solder I8 therein. One end of the loop I'I is secured to the innerend of this neck or basal portion Il so the loop is within the cavity I2and so that the rod portion I t passes outward from the cavity coaxiallythrough the central hole or I6. At the outer endof the thimble theinterior cylindrical wall is provided with an internal annular rabbet I9and the exterior wall is provided with an external peripheral rabbet 20.An end margin of an internal collar 2l is seated in the internal rabbeti9 and sealed, as by solder, to the thimble thereat. The outer end ofthis collar is flanged outwardly, as at 22, so the flange isperpendicular to the axis of the collar and in a plane coincident withthe near wall of the wave guide wall as a continuation of the innersurface thereof.

Within collar 2l the passage through hollow member i is sealed vacuumtight by -a glass bead 26 of predetermined thickness. Preferably aborosilicate glass is employed in conjunction with which the said collar2l and portion 21 of the rod i4 passing through the glass, are made ofmaterial having a corresponding coeicient of expansion, such a materialbeing described in Patent 2,062,335 of December l, 1936, to Howard Scottand sold in the trade under the trade-mark Kovan Outside of and coaxialwith collar 2l isr'a sleeve 28 of adequate strength for supportpurposes, such as brass, which has one end soldered in rabbet and itsother end soldered against the near wall of wave guide I3.

' Within the wave guide, rod HI is provided with an antenna head 2Bpreferably of flaring shape which has a transitional increase indiameter from the portion 21 of the rod toward the outer end of thehead, and being shown as frustoconical and hollow. The controllingfactor for configuration of this antenna head is to obtain a smoothimpedance transition from the coaxial line to the Wave guide, therebyobtaining gradual change without setting up the usual localized highelectrical gradients thereat. This antenna head at its larger end issealed to the far wall of the wave guide i3 for obtaining a goodelectrical connection therewith. For ease of manufacture, said head isshown projecting through the said far wall of the wave guide, therebyenabling the soldering thereof to that wall to be accomplished at theouter side of the wall. This direct attachment of the antenna head ofrod I4 to the wave guide wall completes the coaxial terminal as a closedline. Since the wave guide is operated in the fundamental mode, theaxial length of the tapered antenna is less than half a wave guide wavelength. The thickness of glass bead 2B lengthwise of the rod ispreferably a half wave vlength in dimension in the dielectric mediumcomposing the bead referred to free space wave length.

The interior of the evacuated hollow portion of member l5 is providedwith a transformer section of ypredetermined dimensions. The preferredconstruction utilizes a passage in the neck portion of said member ofsmaller diameter than the diameter of passage or chamber 3| in the bodyof the said member. Furthermore, the passage 30 is of predeterminedlength and formed within a wall which protrudes as a ring 32 at itsupper end into the lower part of the chamber 3|. This combination ofdifferent sizes of passage and chamber and length of smaller passagewith the rabbeted section, and abrupt change of surface directionconstitutes a transformer.

For convenience of reference, the end of the neck portion I1 of themember I5 terminating at the inner wall of the magnetron cavity has beendesignated as in a plane Po, and the upper end of the smaller passageterminated by ring 32 has been designated as in a plane P1, whereasplane of the inner surface of the near wall of the waveguide has beendesignated as plane P2. The open end of the waveguide, which is shownflanged for attachment to any desired instrumentality is designated asat a plane P3. Configuration and distance between planes Po and Pi havedefinite relationship for establishing the proper input admittance atthe base of the loop at plane Po. When once determined and the deviceconstructed, these dimensions and congurations remain constant.Determination of these dimensions and configurations has been realizedby following a practical procedure outlined below, namely:

(a) A constant voltage or current Rieke diagram is run with reference toplane P3 by means of a conventional waveguide coaxial terminal providedwith means whereby variable react-ance and radiation resistance may beobtained. The variable section is preadjusted, first for maximum outputinto a matched load in the waveguide and the Rieke taken, another Riekeis taken with the matching section set at of maximum power under thesame conditions. By way of definition it may be stated a Rieke diagramis a radio frequency output diagram of frequency, power and voltagecontours, for constant current (or voltage, in which case the currentcontours are plotted), as a function of load impedance with respect tosome plane of reference between the load and the base of the couplingloop of the magnetron. The load impedance may be represented on a polardiagram whose radial coordinate denotes the real reflection coefficientsand the angular coordinate denotes the phase angle with respect to thereference plane. One convolution of the angular coordinate correspondsto one-half wavelength. The load impedance may also be represented on acircle diagram, or other suitable tranformation, in which caseresistance and reactance comprise the coordinates.

(b) A suitable operating point is selected from the above data and thecorresponding impedance at the plane P3 obtained from the position ofthe minimum of standing wave pattern from the reference plane Ps of themagnetron, and standing Wave ratio (voltage). Said operating point is anoptimum point 0f operation as defined by the load impedance (orreflection coefficient and position of minimum) on a Rieke diagramreferred to the reference plane of the magnetron, where a definite poweroutput and pulling figure, consistent with a given anode voltage, anodecurrent and magnetic field is obtained characteristic of the load andmagnetron.

(c) The conventional terminal is then reset to either maximum poweroutput or 80% output into a matched line depending upon which settingproduces the better Rieke contour from a functional point of view.

(d) The conventional output terminal (waveguide and coaxial feed) toplane Po is removed from the magnetron intact and to each end areattached lengths of line such that a four terminal net-work may beobtained which is an ideal transformer defined in terms of threeconstants, the transformer constant and two lengths of line.

(e) The operating point defined by the admittance at the plane P3 of theconventional terminal can then be transformed through this network tothe base of the loop of the conventional terminal (plane Po) with theaid of four terminal network theory. z i

(f) Now, with amatched line beyond plane P1 in vthi-:proposed terminal,a transformer between Pn and P1 can be provided to give the desiredadmittance at plane Po.

(g) Next an adjustment of the terminal section looking toward plane P2is required to obtain a standing wave ratio which is substantiallylunity for the wavelength or wavelength band under consideration. lThisis done by providing a dummy terminal between plane P1 and P3 withextended sections of equivalent dimensions, `each withr probes, andthenfeeding the desired energy into the coaxialprobed line to thematched`load in the waveguide.

i The terminal constructed in :accordance 'with my invention presentsthe .proper input admittance to the magnetron, in vacuum, whilemaintaining a low s tanding wave Yratio in the remaining portions `ofthe terminal, 'exposed to the prevailing atmospheric pressure. Since thehief-h electrical gradient of the transformer is within the evacuatedregion, it is not affected by change of external atmospheric-conditionsand the device, inclusive of the waveguide section, functions as well atone elevation as another notwithstanding the atmospheric conditions mayvary in the waveguide.

I claim:

1. An output coupling from an ultra high frequency generator to awaveguide, comprising a hollow member having a basal end next to andprojecting from said generator and said basal end having a longitudinalpassage there-in, said passage having an enlargement thereof at the endof the passage remote from the generator, said hollow member providing achamber of greater diameter than said enlargement, a coaxial innermember extending from said generator to said waveguide coaxially of andthrough said passage, enlargement and chamber, a ring seated in saidenlargement and projecting into said chamber and constituting with thewall of said chamber a transformer, and a vacuum seal for said chamberat the end thereof toward the waveguide whereby the passage, chamber andtransformer are at the same vacuum as the generator, and the locationand seating of said ring in the enlargement enabling the coupling to beassembled with a desired length of ring pro-- truding into the chamberand obtaining desired transformer characteristics.

2. An output coupling from an ultra high frequency generator to awaveguide, comprising a hollow member having a basal end next to andprojecting from said generator and said basal end having a longitudinalpassage therein, said passage having a stepped enlargement at the end ofthe passage remote from the generator, said hollow member providing achamber of greater diameter than said enlargement thereby constituting asecond stepped enlargement of the hollow of said member, a coaxial innermember extending from said generator to said waveguide coaxially of thestepped hollow of said holiow member, a ring seated in the firstmentioned enlargement and projecting into said chamber and constitutingwith the wall of said chamber a transformer, means vacuum sealing theend of said chamber remote from the generator and with the vacuum of thegenerator effective in said chamber and maintained by said means, andthe location and seating of said ring in the first said enlargement andprotruding into the second said enlargement enabling the coupling to beassembled with a desired length of ring protruding .into `the chamber:and obtaining :desired:

transformer characteristics.

3. YAn output coupling from an ultra high frequency .generator to yawaveguide, comprising a hollow member having a basal end next to andprojecting'fr'om said generator and saidbasal vend having a longitudinalpassage therein, said ypassage having .a stepped enlargement at the endof the passage remote from the generator, said hollow y'member providinga chamber yof greater diameter than said enlargement therebyconstituting 'a second stepped enlargement of the hollow of said memberand said second stepped enlargement of rsaid member ybeing againenlargedby a rabbet at the end of said member towardv n the waveguide, acollar seated in :said Vrabbety fand having aange atits end toward thewaveguide, said flange being connected to said waveguide, a coaxial'inner member extendingfrom said generator to said waveguide coaxiallyofand through said hollow member and the passage, enlargement, chamberandrabbet thereof, a ring seated in the first mentioned enlargement andprojecting into said chamber and constituting with the wall of saidchamber a transformer, a glass bead sealed peripherally to said collarand sealed on and to said coaxial inner member and comprising a closurefor said chamber at the end thereof toward the waveguide, the successivestepped enlargements of the hollow of the hollow member enabling thecoupling to be assembled and a ring of desired length seated in the rstenlargement and protruded into the second enlargement for obtainingdesired transformer characteristics.

4. Anoutput coupling from an ultra high frequency generator to awaveguide, comprising a hollow member having a basal end next to andprojecting from said generator and said basal end having a longitudinalpassage therein, said passage having an enlargement thereof at the endof the passage remote from the generator, said hollow member, providinga chamber of greater diameter than said enlargement, a coaxial innermember extending from said generator to said waveguide coaxially of andthrough said passage, enlargement and chamber, a ring seated in saidenlargement and projecting into said chamber and constituting with thewall of said chamber a transformer, said ring having an internaldiameter equal to the diameter of the passage and an outer diameterequal to that of the first said enlargement, and a vacuum seal for saidchamber at the end thereof toward the waveguide whereby the passage,chamber and transformer are at the same vacuum as the generator, and thelocation and seating of said ring in the enlargement enabling thecoupling to be assembled with a desired length of ring protruding intothe chamber and obtaining desired transformer characteristics.

5. An output coupling from an ultra high frequency generator to awaveguide, comprising a hollow member having a basal end next to andprojecting from said generator and said basal end having a longitudinalpassage therein, said passage having a stepped enlargement at the end ofthe passage remote from the generator, said hollow member providing achamber of greater diameter than said enlargement thereby constituting asecond stepped enlargement of the hollow of said member and said secondstepped enlargement of said member being again enlarged by a rabbet atthe end of said member toward the waveguide, a collar seated in saidrabbet and having a flange at its end toward the waveguide, said flangebeing connected to said waveguide,

7 a coaxial inner member extending from said generator to said waveguidecoaxially of and through said hollow member and the passage,enlargement, chamber and rabbet thereof, a ring seated in the rstmentioned enlargement and projecting into said chamber and constitutingwith the 1 wall of said chamber a transformer, a glass bead sealedperipherally to said collar and sealed on and to said coaxial innermember and comprising a closure for said chamber at the end thereoftoward the waveguide, a sleeve coaxial with and at the outside of saidcollar, said sleeve being rigidly connected at its ends to the saidhollow member and waveguide respectively and protecting said collar fromstrains and distortions, the successve stepped enlargements of thehollow of the hollow member enabling the coupling to be assembled and aring of desired length seated in the first enlargement and protrudedinto the second enlargement for obtaining desired transg@ formercharacteristics.

' ERNEST C. OKRESS.

REFERENCES CITED The following references are of record in the iile ofthis patent:

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